1. Field of the Invention
The present invention relates to a power-saving control of a network device.
2. Description of the Related Art
In recent years, energy-saving standards have become stricter and in order to comply with the standards, some methods of shutting off the power supply of a CPU in a power-saving mode have already come into practical use.
On the other hand, in printers or multifunctional devices for network, it has become increasingly necessary to return from the power-saving mode to a normal operation mode at high speed. Further, since the sizes of programs of recent multifunctional devices have been increasing, if all programs are stored on a ROM, the costs increase. Accordingly, in some of the multifunctional devices, the hard disk is commonly used as an image storage unit, and the programs are also stored on a part of the region of the hard disk.
However, in this case, after start-up, the programs are downloaded from the hard disk to a RAM, and then, the programs are executed on the RAM. As a result of the using the RAM to store such programs, the processing speed of the device becomes slower bringing about a factor which conflicts with the above requirement of high-speed return.
Therefore, a method of shutting off the power supply of CPU while retaining a program expanded on a RAM has been proposed (Japanese Patent Application Laid-open No. 2004-005029). In such a method in which the power-saving mode is realized by shutting off the power supply of CPU, with respect to some network protocols that the device supports, there arises a problem described below. For example, when the APPLETALK network protocol is implemented, in each device on the network which uses the APPLETALK network protocol, a protocol address is dynamically changed.
Accordingly, the protocol address which is used by the device can be allocated to the other device while the device is entering the power-saving mode. That is, the protocol address used before entering the power-saving mode overlaps with the protocol address of the other device, and the protocol address cannot be used any more.
To solve the problem, a device which supports the APPLETALK network protocol tries to frequently return from the power-saving mode and monitor packets on the network in order to determine whether there is no problem with the protocol address currently being used (whether it is possible to continue to be used). However, if the device frequently returns from the power-saving mode, it is not substantially possible to enter the power-saving mode to shut down the power supply of the CPU.
Next, as an example of a dynamic protocol address, a DHCP protocol of the TCP/IP is taken. In the case of the DHCP protocol, it is necessary to constantly request a server to update an IP address which is acquired by a device from a DHCP server. Accordingly, if the intervals of the IP address update are short, it is also difficult to enter the power-saving mode.